Caption:
Iodine reduction by tin, 1 of 3. Tin(II) sulphate (SnSO4) solution has pale yellow colour (left vial). Iodine (I2) dissolved in water with added potassium iodide (KI) and polyvinyl alcohol has deep blue colour (right vial). When tin(II) sulphate solution is added drop by drop to the iodine solution (middle vial), it becomes colorless, as I2 is reduced to I- and Sn2+ is oxidized to Sn4+: Sn2+ + I2 -> Sn4+ + I-.